Generally, as a method of forming a coating layer on a base film, slot die coating methods have been used.
FIG. 1 is a configuration diagram schematically illustrating a conventional slot die coating used in the slot die coating method.
As shown in FIG. 1, coating is carried out on the surface of a substrate film 2 wound around a roll 1 using a slot die 3. A coating layer 4 is formed on the surface of the base film 2 by the slot die 3. In this case, a vacuum chamber 5 is attached at a front end of the slot die 3, and the vacuum chamber 5 serves to increase the stability of the coating by creating a vacuum environment locally.
However, since the vacuum chamber 5 does not come in close contact with the base film 2 in order to form the coating layer, a certain gap D should be made. Due to the flow of the air inflow through the gap D, high velocity flow occurs in the vacuum chamber 5, the high velocity flow cause turbulent flow, and thus the pressure in the vacuum chamber 5 is not constant but oscillates. Therefore, if the pressure in the vacuum chamber oscillates, the coating of the base film is unstable and thus the quality of a product is poor.
Accordingly, a slot die coating apparatus which can fundamentally solve this problem urgently needs to be developed.
The following patent documents 1 and 2 disclose slot die coating apparatuses.